The invention relates to a saturated high-pressure sodium discharge lamp provided with a ceramic discharge vessel, in which sodium, mercury and xenon are present, of which the xenon is at a pressure of at least 26.7 kPa (200 torr) at 300K, while the lamp generates in the operating condition a light spectrum, in which at a wavelength of 589.3 nm an absorption band is present, on either side of which spectral flanks are disposed each having a respective maximum, a wavelength difference .DELTA..lambda. occurring between the said maxima.
A lamp of the kind mentioned in the opening paragraph is known from British Patent Specification 1,587,987 which corresponds to U.S. Pat. No. 4,260,929. The known lamp, which is frequently used inter alia in public illumination, is an efficient light source. During lamp operation, the vapor pressure of sodium and mercury is controlled by the cold spot of the discharge vessel because all of the sodium and mercury is not evaporated. The xenon serves as buffer gas, as a result of which the radiation efficiency and hence the luminous efficacy are improved with respect to high-pressure sodium lamps containing rare gas as starting gas, i.e. at a pressure up to 6.7 kPa (50 torr). The light spectrum generated in the operating condition by the two kinds of high-pressure sodium lamps is very uniform.
However, the light spectrum generated by these lamps comprises a comparatively small contribution in the blue part. This is an obstacle for the use of these lamps in certain applications.